Cyclical necking machines for producing, for example, metal hollow bodies are currently used predominantly in a horizontal design, that is to say the working movement takes place substantially horizontally, modified vertical presses having been used at the starts of the drawing-in operation.
The cans (as one example of a metal hollow body) are conventionally as a rule fed to the machine, coming from below via a belt (for practical considerations, since other regions then remain more readily accessible) via a feed device (as a rule, a vacuum drum), are transferred from there into a holding apparatus which for its part is positioned on a rotary table which is driven cyclically in a synchronous manner with respect to the working process. The can is thus fed to the different working stages one after another, until finally all processing steps which are provided in the machine have been executed. Finally, the can is removed from the working region of the machine via a discharging device which is comparable with the feed apparatus, and are transferred via a belt to the next machine.
Machines having rotary tables of between 20 and 48 stations are currently offered and operated commercially, 50 stations already having been provided.
The smaller machines come from the time when the metal containers were made from Al99.5 and only a shoulder was shaped which served to draw in the can diameter down to the diameter possessed by the valve to be attached, in the exemplary case of aerosol cans. With increasing diameters of the containers and increasingly complex shapes, larger machines were developed, by way of which these requirements should be met in a machine, since only a certain degree of deformation (ultimately a change in diameter) can be achieved per deforming step. More complicated or greater deformation therefore requires more stations.
In later years, the containers made from Al99.5 were joined by containers made from alloyed aluminum or else from steel with relatively thin wall thicknesses (called “thin-walled containers”). As a result of the material properties, the degrees of deformation which can be achieved here per stage are only approximately half as great at most, however, with the result that at least twice as many stations are required for the same shape in comparison with an identical “thick-walled” container made from Al99.5.
There is therefore the fundamental aim for it to be possible to provide a greater number of stations for a drawing-in operation.
According to the current prior art, a first approach consists in combining a plurality of (small) known machines with one another (that is to say, in series).
One disadvantage of said first approach consists in that a comparatively large amount of space is required, a further disadvantage lying in the high costs per station, since most of the components have to be provided multiple times. Furthermore, the operation of a plurality of machines also results in a higher energy requirement, which has an unfavorable effect on the environmental balance of the hollow body. It is disadvantageous, furthermore, that the cans have to be removed from the holding chucks at the exit of a machine and have to be received again in the following machine; said receiving should ideally be performed in exactly the same position in relation to the chuck as previously, since otherwise the orientation of the hollow body with respect to its longitudinal axis would undesirably be lost (rotation of the hollow body would therefore occur). A further complexity consists in that the machines are synchronized or are decoupled to a sufficient extent by way of small buffer storage sections. Said buffer storage sections are, for example, bowl feeders, in which the cans are positioned in a merely very restrictedly arranged manner. Furthermore, each machine transfer increases the risk of damage to the hollow body and therefore an increase in the rejects.
A second known approach consists in providing larger and larger machines; 50 stations on one rotary table in the near future.
This approach reaches its limits in conjunction with the manageable handling and the moving masses, the feasible number of stations nevertheless being unsatisfactory for a number of products, in particular from the field of thin-walled containers. A particular problem consists in that the transverse acceleration on the machine increases considerably during rotation of the rotary table with an increasing size; said movement can be compensated for only in a very complicated manner, since it is intermittent.